1. Field of the Invention
The present invention relates in general to servo control systems and in particular to a machine tool numerical control system with position encoder feedback.
2. Description of the Prior Art
Numerical control systems for controlling machine tools can be operated in either open-loop or closed-loop configurations. In the open-loop configuration, control signals are generated to a drive means for moving the machine tool to a selected position. However, no check is made by this system to determine if the machine tool has actually reached the selected position. In the closed-loop system, a feedback signal representing the actual position of the machine tool is compared with a control signal representing the selected position to generate an error signal which is utilized to move the machine tool to the selected position.
One type of device which is commonly used to generate the feedback signal is an electromechanical device known as an encoder. The encoder is mechanically coupled to the machine tool and generates a series of pulses which are utilized to determine the actual position of the machine tool. If the actual position of the machine tool is not equal to the selected position of the machine tool, an error voltage is generated to correct the machine tool position.